(a) Field of the Invention
The present invention relates to a method and an apparatus for detecting a signal, and more particularly, to a method and apparatus for detecting a signal in a multi-input multi-output wireless communication system.
(b) Description of the Related Art
A multiple input multiple output (hereinafter referred to as “MIMO”) communication system using multiple transmission/reception antennas and Bell Labs layered space time (BLAST) technology in order to transmit higher-speed data without increasing a bandwidth.
A transmitter transmits different data through a plurality of antennas, and a signal of each of the antennas undergoes independent fading. In the BLAST technology, a receiver discriminates transmitted data through proper signal processing, but signals received from other antennas are overlapped with each other to thereby generate inter-antenna interference (IAI) which is an interference factor increasing the number of errors.
The receiver generally performs steps of detection ordering, interference nulling, and interference cancellation in order to detect the transmitted data.
First, the detection ordering step is a step of determining a detection order. This uses a scheme of selecting and detecting a signal having the largest signal-to-noise ratio for each detection step.
Next, the interference nulling step is performed. In this step, an appropriate weight vector for nulling the remaining signals in order to detect one signal determined during the detection ordering step is multiplied by a received signal vector. The weight vector can be acquired by zero-forcing (ZF) or a minimum mean squared error (MMSE) standard.
Next, the detection signal is regenerated and subtracted from the received signal vector. This step is the interference cancellation step. The reason for the signal processing is to, in the case where a signal is recovered without an error, improve the signal-to-noise ratio by removing an unnecessary interference signal at the time of detecting the subsequent signal.
As such, after the detection order is determined by firstly selecting a signal having the highest signal-to-noise ratio, each signal is detected while multiplying the weight vector by the ZF or MMSE standard each time, and the signal detection step of removing the interference by the detected signal from the received signal is consecutively performed until all signals are detected.
At this time, a step of determining an optimal signal detection order and determining a nulling vector is performed by repeatedly processing acquisition of an inverse matrix of a channel matrix. However, performing the inverse matrices of numerous channel matrices in order to achieve optimal performance cannot be implemented in hardware. In order to implement it, there is a scheme of substituting an inverse matrix processing step or reducing a calculation amount by applying Gram-Schmidt orthogonalization to the channel matrix.
The GSO scheme is flexible in that determining the detection order and determining the nulling vector can be separated from each other. However, the GSO scheme is very sensitive to an error generated during the first signal detection step. More specifically, when an error is generated during the first signal detection step, an error amplification effect in which the error generated at that time is amplified during the subsequent signal detection step is caused, thereby causing a serious problem in the performance of a system.
It is necessary to more accurately determine the signal detection order.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.